On 2022-04-22 10:28, Melissa Wen wrote:
On 04/21, Harry Wentland wrote:
On 2022-04-21 15:20, Melissa Wen wrote:
On 04/21, Harry Wentland wrote:
On 2022-04-21 10:37, Melissa Wen wrote:
Hi all,
I'm examining how DRM color management properties (degamma, ctm, gamma)
are applied to AMD display drivers. As far I could understand thanks
Nicholas documentation on amdgpu_dm/amdgpu_dm_color, DC drivers have
per-plane color correction features:
Hi Harry,
Wow, thanks so much for all details!
DC programs some of the color correction features pre-blending but
DRM/KMS has not per-plane color correction properties.
See this series from Uma Shankar for an RFC on how to introduce those
properties for 1D LUTs and CSC matrix:
https://patchwork.freedesktop.org/series/90826/
Bhanuprakash has a series of IGT tests for these properties:
https://patchwork.freedesktop.org/series/96895/
I've rebased these on amd-staging-drm-next and maintain a kernel and IGT
branch with these patches:
https://gitlab.freedesktop.org/hwentland/linux/-/tree/color-and-hdr
https://gitlab.freedesktop.org/hwentland/igt-gpu-tools/-/tree/color-and-hdr
We've had many discussions with Weston guys on this. In order to merge the
kernel properties we need a canonical userspace implementation that are
using it. Weston guys are working towards that but if you want to suggest a
different userspace to serve as that vehicle I'd be all ears. :)
Note that in order to show this all working we also need a Wayland Protocol
update.
See
https://gitlab.freedesktop.org/pq/color-and-hdr
https://gitlab.freedesktop.org/swick/wayland-protocols
https://gitlab.freedesktop.org/wayland/weston/-/issues/467
So, I've followed these discussions (until the issue on naming) because
initially I considered it addresses our current goals for color
correction. But after some discussions, what we are targeting is a 3D
LUT after blending (per-CRTC). I found past proposals on dri-devel
[1][2] to extend the DRM CRTC color management properties, but they
didn't move forward and were never applied.
They're stuck in limbo until we have an upstream userspace
implementation that's making use of them.
Yes... afaiu, the basic requirements for all of these changes are IGT
tests + open userspace usage, right?
Correct. See [1] and [2].
[1] https://www.kernel.org/doc/html/latest/gpu/drm-kms.html#requirements
[2]
https://www.kernel.org/doc/html/latest/gpu/drm-uapi.html#open-source-userspace-requirements
* - Input gamma LUT (de-normalized)
* - Input CSC (normalized)
* - Surface degamma LUT (normalized)
* - Surface CSC (normalized)
* - Surface regamma LUT (normalized)
* - Output CSC (normalized)
so DM is "adapting" those DRM per-CRTC properties to fit into three of
these color correction stages, which I guess are the surface stages:
* - Surface degamma LUT (normalized)
* - Surface CSC (normalized)
* - Surface regamma LUT (normalized)
I'm trying to understand what this mapping is doing. A comment mentions
that is not possible to do these color corrections after blending, so,
the same color correction pipe is performed on every plane before
blending? (is the surface the plane?) Does this adaptation affect the
expected output? Moreover, is there something that I misunderstood? :)
What's possible to do before and after blending has changed quite a bit
between DCN generations. We program the CRTC Gamma and CTM after blending.
See attached picture for a view relating the color bits between the DRM
interface, DC interface and DCN 3.0 HW blocks.
This picture is really enlightening, thanks!
You said it changes between generations, therefore, I can't consider the
DCN 2.x family follow the same mapping, right? If so, can you share the
main differences for a DCN 2.x regarding per-CRTC properties?
See attached diagram for DCN 2.0.
Thanks again!
That said, if the DRM color mgmt supports per-CRTC 3D LUT as the last
Where do you see 3D LUT support in DRM? Is there a new proposal that I've
missed?
So, it's exactly what I aim to work: a proposal to add 3D LUT to the
current range of DRM per-CRTC color properties. But I also need to
understand how this property will be mapped to AMD display once it
exists in the DRM framework.
Ah, nice to see. :)
One of the things that caught my attention after seeing the attached
picture is the position of 3D LUT. I was expecting to see the 3D LUT
correction after gamma correction. Is this position a particularity of
DCN 3.0 (that varies between hw) or was I expecting a wrong color
correction pipeline at all?
Before DCN 3.0 there was no 3D LUT after blending.
By comparing these diagrams, I'm curious: in case we have a per-CRTC 3D
LUT support on DRM, DCN 2.0 generations would initially map this
property as a pre-blending property on DPP (currently the same approach
for CTM, for example), right? But after we also have a per-plane color
management property, those per-CRTC property would be ignored? And how
about degamma for both generations? No problem if there isn't an answer
yet (many if's), but it may help me to think of a more generic solution.
We'll need to define what the expectations are for the API
implementations in DRM drivers, as well as for the implementing userspace.
The way I think about this it might make sense to introduce a 3D LUT on
a drm_plane, as well as on drm_crtc and a driver exposes whatever HW
supports. Userspace can then figure out what it can use based on driver
support.
It should be possible to use pre-blending 3D LUTs to accomplish the same
as a post-blending 3D LUT, but we might need the ability to linearize
before blending, but after applying the 3D LUT, and de-linearize after
blending again. Something like this:
3dlut > linearize (1dlut) > blend > de-linearize (1dlut) > output
Instead of this for the post-blending 3dlut:
linearize (1dlut) > blend > de-linearize (1dlut) > 3dlut > output
Though it depends a bit on the color model in the compositor or
rendering app.
Note in the diagram that our HW (and DC interface) have a Shaper LUT
available before the 3D LUT. You could expose if you want to shape your
content post-blending before applying the 3D LUT.
The 3D LUT is most effective when it's in non-linear space. Currently
DRM has no way to specify a way for drm_plane to be linearized (see notes
(1) and (2)) so it is assumed that you're blending in non-linear space and
therefore your pixels would already be non-linear going into your 3D LUT.
(1) unless you use the drm_plane PWL API that was proposed
(2) amdgpu_dm is currently setting the drm_crtc degamma LUT on the
DC plane. This might lead to unexpected behavior when using
multiple planes (though I believe gamescope is making use of
this behavior).
Thanks for raising these points. In fact, I was considering unexpected
behavior when I saw this DRM <-> DC mapping. >>
Have you looked at [1] yet? It might provide a good example on how to
define a 3D LUT. For AMD HW you'll want a 17x17x17 LUT.
[1] http://intel.github.io/libva/structVAProcFilterParameterBuffer3DLUT.html
Not yet, but it seems helpful. I'll take as a reference... until now,
I've only examined details on DC drivers.
Sounds great.
Harry
Thanks,
Melissa
Harry
Melissa
[1] https://lore.kernel.org/all/20201221015730.28333-1-laurent.pinchart+renesas@xxxxxxxxxxxxxxxx/
[2] https://github.com/vsyrjala/linux/commit/4d28e8ddf2a076f30f9e5bdc17cbb4656fe23e69
I'm thinking of putting a 3D LUT proposal together but haven't gotten around
to it yet. We'll want a pre-blending 3D LUT, and possible a programmable
post-blending one as well.
Thanks,
Harry
step of color correction, I don't see how to accommodate it in the
mapping above, but I see DC already supports programming 3D LUT on DPP.
Once DRM has the 3D LUT interface and DM mapped it as a DPP property,
the 3D LUT will be at the end of the color correction pipeline? Is there
anything I need to worry about mapping DRM 3D LUT support? Or any
advice?
Thanks in advance,
Melissa
